Powerpoint Slides - Suraj @ LUMS
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MPLS Protection Routing:
A Tutorial
Zartash Afzal Uzmi
First slide…
Questions?
Ask when you have them!
Jan 13, 2006
Lahore University of Management Sciences
2
Outline
Background
Network Services and QoS
Architectural Requirements
IP and MPLS
Introduction to protection and restoration routing
Terminology
Local Protection: Types of Backup Paths Fault Models
Backup Bandwidth Sharing
Activation sets
Protection routing framework
Components
Typical example
Evaluation and Experimentation
Jan 13, 2006
Lahore University of Management Sciences
3
Outline
Background
Network Services and QoS
Architectural Requirements
IP and MPLS
Introduction to protection and restoration routing
Terminology
Local Protection: Types of Backup Paths Fault Models
Backup Bandwidth Sharing
Activation sets
Protection routing framework
Components
Typical example
Evaluation and Experimentation
Jan 13, 2006
Lahore University of Management Sciences
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Network Traffic and Services
Network Traffic today
New and interactive applications are emerging
Not what it was 10 years ago
Multimedia intensive
Internet telephony
Videoconferencing
Streaming media (voice and video)
Remote collaboration (e.g., remote desktop)
Many new applications are real-time
More and more users of these applications
Burstiness behavior has changed over the years!
Jan 13, 2006
Lahore University of Management Sciences
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Current Network Architecture
Internet is popular because
Internet is inexpensive because
It uses resource sharing
by means of statistical multiplexing
Current Internet architecture
It is inexpensive
Uses packet switches with buffers
Required buffer size is primarily determined by a
random traffic pattern
Buffer size optimization
Too low High drop rate
Too high High delay
Jan 13, 2006
Lahore University of Management Sciences
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Architectural Requirements
Emerging applications
Under normal conditions
We are worried about the buffers used in two-way
interactive applications
When resources fail
Two-way interactive communications
One-way streaming media type applications
We are also worried about the one-way applications
Current Internet architecture is not suitable for
new and emerging applications
New architectures are being researched
Jan 13, 2006
Lahore University of Management Sciences
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Architectural Requirements
New network architectures
Experience with networks
All circuit-switched?
Mix of packet-switch and “circuit-switch-like”
Bigger buffers are required when there is more
randomness and more aggregation
Should use circuits at places where we see more
aggregation
Example: 100x100 project
Edge network is packet-switched
Core network is virtual-circuits
Jan 13, 2006
Lahore University of Management Sciences
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IP versus MPLS
In IP Routing, each router makes its own routing
and forwarding decisions
In MPLS:
source router makes the routing decision
Intermediate routers make forwarding decisions
A path is computed and a “virtual circuit” is established
from ingress router to egress router
An MPLS path or virtual circuit from source to
destination is called an LSP (label switched path)
Jan 13, 2006
Lahore University of Management Sciences
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Outline
Background
Network Services and QoS
Architectural Requirements
IP and MPLS
Introduction to protection and restoration routing
Terminology
Local Protection: Types of Backup Paths Fault Models
Backup Bandwidth Sharing
Activation sets
Protection routing framework
Components
Typical example
Evaluation and Experimentation
Jan 13, 2006
Lahore University of Management Sciences
10
Protection and Restoration
Restoration
Protection
Pre-determined recovery – backup paths “in advance”
Primary and backup are provisioned at the same time
IP supports restoration
On-demand recovery – no preset backup paths
Example: existing recovery in IP networks
Because it is datagram service
MPLS supports restoration as well as protection
Because it is virtual-circuit service
Jan 13, 2006
Lahore University of Management Sciences
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Restoration in IP network
In traditional IP, what happens when a link
or node fails?
Failure information needs to be disseminated in
the network
During this time, packets may go in loops
Restoration latency is in the order of seconds
We look for protection possibilities in an
MPLS network, but…
First we need to look at the QoS requirements
Jan 13, 2006
Lahore University of Management Sciences
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QoS Requirements
Bandwidth Guaranteed Primary Paths
Bandwidth Guaranteed Backup Paths
BW remains provisioned in case of network failure
Minimal “Protection or Restoration Latency”
Protection/Restoration latency is the time that elapses
between:
“the occurrence of a failure”, and
“the diversion of network traffic on a new path”
Restoration is generally SLOWER than protection
Jan 13, 2006
Lahore University of Management Sciences
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Protection in MPLS
First we define Protection level
Path protection
Also called end-to-end protection
For each primary LSP, a node-disjoint backup LSP is set up
Upon failure, ingress node diverts traffic on the backup path
Local Protection
Upon failure, node immediately upstream the failed element
diverts the traffic on a “local” backup path
Path Protection More Latency
Local Protection Less Latency
Jan 13, 2006
Lahore University of Management Sciences
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Protection in MPLS
Path Protection
S
1
2
3
D
This type of “path Protection”
still takes 100s of ms.
Primary Path
Backup Path
Jan 13, 2006
We may explore “Local Protection” to
quickly switch onto backup paths!
Lahore University of Management Sciences
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Local Protection: Fault Models
Link
Protection
Node
Protection
Element
Protection
Jan 13, 2006
A
B
C
D
A
B
C
D
A
B
C
Lahore University of Management Sciences
D
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Protection Modes
1+1 protection
1:1 protection
A backup path protects a single LSP (or a portion of a
single LSP)
N:1 protection
Flow sent on two separate disjoint paths
Receiver responsible for choosing one of the two
A backup path protects one link or one node or both
Overlapping portions of many LSPs are protected by a
single backup path
Applicable for local protection only
N:M protection (M<N)
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Lahore University of Management Sciences
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nhop and nnhop paths
LOCAL PROTECTION
nnhop
A
B
D
C
E
nhop
PLR: Point of Local Repair
Primary Path
Backup Path
Jan 13, 2006
All links and all nodes are protected!
Lahore University of Management Sciences
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Opportunity cost of backup paths
Local Protection requires that backup paths are setup in
advance
Upon failure, traffic is promptly switched onto preset
backup paths
Bandwidth must be reserved for all backup paths
This results in a reduction in the number of Primary LSPs
that can otherwise be placed on the network
Can we reduce the amount of “backup bandwidth” but
still provide guaranteed backups?
Jan 13, 2006
Lahore University of Management Sciences
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BW Sharing in backup Paths
Example:
Sharing
LSP1
A
BW: X
B
X
X
E
LSP2
G
F
X+Y
Y
C
X
max(X, Y)
BW: Y
Y
D
Primary Path
Backup Path
Jan 13, 2006
Lahore University of Management Sciences
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Activation Sets
A
A
E
B
C
C
D
D
Activation set for node B
Jan 13, 2006
E
B
Activation set for link (A,B)
Lahore University of Management Sciences
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Outline
Background
Network Services and QoS
Architectural Requirements
IP and MPLS
Introduction to protection and restoration routing
Terminology
Local Protection: Types of Backup Paths Fault Models
Backup Bandwidth Sharing
Activation sets
Protection routing framework
Components
Typical example
Evaluation and Experimentation
Jan 13, 2006
Lahore University of Management Sciences
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Protection Routing Frameworks
We look to answer the following questions?
Who computes the primary path?
What is the fault model (link, node, or element protection)?
Where do the backup paths originate?
Who computes the backup path?
At what point do the backup paths merge back with the
primary path
What information is stored locally in the nodes/routers
What information is propagated through routing protocols
What if a primary path can not be fully protected
The goal is almost always to maximize bandwidth sharing
Performance criteria is almost always the maximum number
of primary LSPs that can be placed on the network
Jan 13, 2006
Lahore University of Management Sciences
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Evaluation & Experimentation
Traffic Generation
Rejected Requests Experiments
Use existing or emerging traffic models
Consider call holding times and multi-service traffic
Generate a set of LSP requests
Measure the number of rejected requests
Simulate on various topologies
Network Loading Experiments
Set link capacities to infinity
Measure the total bandwidth required to service a given
set of LSP requests
Simulate on various topologies
Jan 13, 2006
Lahore University of Management Sciences
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Recent Trends
Preemption of lower class traffic
Multilayer recovery
We can “almost” deal with recovery at a single protocol
layer
What if we intend to provide recovery at multiple
protocol layers?
For multilayer recovery, we need to consider
these additional issues:
Interworking of layers
Local information stored at each node of each layer
Recovery provided by each individual layer
Signaling mechanism from one layer to another
Effects on bandwidth sharing (if sharing is used)
Jan 13, 2006
Lahore University of Management Sciences
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We are not done, yet…
Questions & Answers
Jan 13, 2006
Lahore University of Management Sciences
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Extra Stuff!
Example: A Protection Routing
Architecture
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Lahore University of Management Sciences
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Extent of BW Sharing: oAIS
More Information propagated More potential for BW sharing
Aggregate Information Scenario (AIS)
Fij: Bandwidth reserved on link (i, j) for all primary LSPs
Gij: Bandwidth reserved on link (i, j) for all backup LSPs
Rij: Bandwidth remaining on link (i, j)
Optimized AIS (oAIS) – (Hij instead of Fij)
Hij:
Maximum bandwidth reserved on any one link by all
backup paths spanning link (i, j)
Also propagate Gij and Rij
Jan 13, 2006
Lahore University of Management Sciences
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oAIS versus AIS: Example
LSP Request-1 (src, dst, bw) = (A, C, 4)
D
GAF=4
E
F
FAB=4
A
HAB=4
B
C
G
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Lahore University of Management Sciences
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oAIS Example
LSP Request-2 (src, dst, bw) = (A, C, 5)
D
GAF=4
E
F
FAB=4
=9
A
B
C
HAB=4
=5
GAG=5
G
Jan 13, 2006
Lahore University of Management Sciences
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oAIS Example
LSP Request-3 (src, dst, bw) = (D, E, 7)
FDE=7
D
GAF=7
=4
E
F
FAB=9
A
B
C
HAB=5
GAG=5
G
Jan 13, 2006
Lahore University of Management Sciences
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oAIS Example
LSP Request-4 (src, dst, bw) = (A, C, 6)
Need to Evaluate cost of all possible backup paths?
How much BW is shareable on (A, F)?
D
AIS:
Shareable = max(0, GAF - FAB)
= GAF - min(GAF, FAB) = 0
Additional resv = 6
oAIS: (HAB ≤ FAB)
Shareable = GAF - min(GAF, HAB) = 2
Additional resv = 6 - 2 = 4
CIS: (link (A,B) knows BWred)
Shareable = GAF - BWred = 7 - 4 = 3
Additional resv = 6 - 3 = 3
Jan 13, 2006
GAF=7
FDE=7
E
F
FAB=9
A
B
C
HAB=5
GAG=5
Lahore University of Management Sciences
G
32
Single Link Protection: Network 1
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Lahore University of Management Sciences
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Single Link Protection: Network 1
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Single Link Protection: Network 2
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Single Link Protection: Network 2
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Single Node Protection: Network 1
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Lahore University of Management Sciences
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Single Element Protection: Network 1
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Lahore University of Management Sciences
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More Extra Stuff!
Bandwidth Sharing Model for
oAIS
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Lahore University of Management Sciences
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A Bandwidth Sharing Model
(Simplified for the Link Protection Fault Model)
Recall the definition of nhop paths
Link
Protection
A
B
C
D
Primary Path
Backup Path
Jan 13, 2006
All links are protected!
Lahore University of Management Sciences
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Bandwidth Sharing Model
Previous:
Aij:= Set of all primaries traversing through (i, j)
Buv:= Set of all backups traversing through (u, v)
New definition (specialized for link protection
case):
Aij:= Set of all primaries traversing through (i, j)
Buv:= Set of all nhop paths traversing through (u, v)
µij:= Set of all nhop paths that span (i, j)
ijuv:= Buv ∩ µij (set of paths falling on (u,v) if (i,j) fails)
Jan 13, 2006
Lahore University of Management Sciences
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Bandwidth Sharing Model
u
3
i
OLD MODEL:
Aij = {R, B}
Buv = {R, B, …}
Aij ∩ Buv= {R, B}
|| Aij ∩ Buv || = 2+7 = 9
Un-shareable = 9
Shareable = 10 - 9 = 1
Jan 13, 2006
v
j
RED=7
BLU=2
GRN=3 (New Request)
Guv = 10
k
NEW MODEL:
Aij = {R, B}
Buv = {nhijr, nhijb, …}
(nhops through (u, v))
µij = {nhijr, nhijb, …}
(nhops spanning (i, j))
ijuv = µij ∩ Buv= {nhijr, nhijb}
|| ijuv || = 2 + 7 = 9
(Un-shareable)
Shareable = Guv - || ijuv || = 10 - 9 = 1
Lahore University of Management Sciences
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Bandwidth Sharing Model
u
3
i
OLD MODEL:
Aij = {R, B}
Buv = {R, B, …}
Aij ∩ Buv= {R, B}
|| Aij ∩ Buv || = 2+7 = 9
Un-shareable = 9
Shareable = 10 - 9 = 1
Jan 13, 2006
v
j
RED=7
BLU=2
GRN=3 (New Request)
Guv = 10
k
NEW MODEL:
Aij = {R, B}
Buv = {nhijr, nhjkb, …}
(nhops through (u, v))
µij = {nhijr, nhijb, …}
(nhops spanning (i, j))
ijuv = µij ∩ Buv= {nhijr}
|| ijuv || = 7
(Un-shareable)
Shareable = Guv - || ijuv || = 10 - 7 = 3
Lahore University of Management Sciences
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Last slide…
Thank you!
Questions?
Jan 13, 2006
Lahore University of Management Sciences
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